Patch "x86/debug: Handle warnings before the notifier chain, to fix KGDB crash" has been added to the 4.13-stable tree

Patch "x86/debug: Handle warnings before the notifier chain, to fix KGDB crash" has been added to the 4.13-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/debug: Handle warnings before the notifier chain, to fix KGDB crash

to the 4.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-debug-handle-warnings-before-the-notifier-chain-to-fix-kgdb-crash.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From b8347c2196492f4e1cccde3d92fda1cc2cc7de7e Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Date: Mon, 24 Jul 2017 13:04:28 +0300
Subject: x86/debug: Handle warnings before the notifier chain, to fix KGDB crash

From: Alexander Shishkin <alexander.shishkin@linux.intel.com>

commit b8347c2196492f4e1cccde3d92fda1cc2cc7de7e upstream.

Commit:

  9a93848fe787 ("x86/debug: Implement __WARN() using UD0")

turned warnings into UD0, but the fixup code only runs after the
notify_die() chain. This is a problem, in particular, with kgdb,
which kicks in as if it was a BUG().

Fix this by running the fixup code before the notifier chain in
the invalid op handler path.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Ilya Dryomov <idryomov@gmail.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Link: http://lkml.kernel.org/r/20170724100428.19173-1-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kernel/traps.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -221,9 +221,6 @@ do_trap_no_signal(struct task_struct *ts
 		if (fixup_exception(regs, trapnr))
 			return 0;
 
-		if (fixup_bug(regs, trapnr))
-			return 0;
-
 		tsk->thread.error_code = error_code;
 		tsk->thread.trap_nr = trapnr;
 		die(str, regs, error_code);
@@ -304,6 +301,13 @@ static void do_error_trap(struct pt_regs
 
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 
+	/*
+	 * WARN*()s end up here; fix them up before we call the
+	 * notifier chain.
+	 */
+	if (!user_mode(regs) && fixup_bug(regs, trapnr))
+		return;
+
 	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
 			NOTIFY_STOP) {
 		cond_local_irq_enable(regs);


Patches currently in stable-queue which might be from alexander.shishkin@linux.intel.com are

queue-4.13/x86-debug-handle-warnings-before-the-notifier-chain-to-fix-kgdb-crash.patch